Various circuit topologies for converters are known in order to generate a current suitable for semiconductor light sources, such as light-emitting diodes, from a mains AC voltage. The converters usually have a two-stage construction. A first stage operates as power factor correction in order to effect sinusoidal mains power consumption which is prescribed in many countries. This first stage generates a constant output voltage which is often referred to as an intermediate circuit voltage. This stage is often in the form of a boost converter. On the basis of this output voltage, the second stage generates a current which is suitable for the semiconductor light sources.
For this purpose, a buck converter is often used as the circuit topology. However, the choice of these converter topologies also results in disadvantages. The combination of two switching regulators is very complicated and expensive to produce. Therefore, many proposals were presented of how the circuit topology can be simplified and the production costs can be reduced. For example, EP 2 315 497 A1 proposed the practice of replacing the buck converter with a linear regulator. However, this is possible only if the semiconductor light sources to be operated have a sufficiently high voltage since the output voltage in the boost converter is very high owing to the system.